A related art vehicle ultrasonic parking assistance apparatus is an apparatus that transmits an ultrasonic wave to an object, and processes a signal reflected from the object to calculate distance information to the object. The related art vehicle ultrasonic parking assistance apparatus amplifies power of the signal reflected from the object to determines noise, and generates a high-voltage signal by using a transformer to transmit a high-power ultrasonic wave.
That is, the related art vehicle ultrasonic parking assistance apparatus transmits/receives a sound wave having a frequency of 20 kHz to 80 kHz by using an ultrasonic converter that converts a voltage into a sound pressure and converts a sound pressure into a voltage.
Generally, as an intensity of a transmission sound wave increases, a level of a signal reflected from an object increases, the related art vehicle ultrasonic parking assistance apparatus inputs an alternating current (AC) voltage of 20 V to 100 V or more to the ultrasonic converter so as to prevent an object from being inaccurately recognized or from not being recognized.
However, since a level of a voltage used in general controllers is limited to a vehicle battery voltage 16V or less, the related art vehicle ultrasonic parking assistance apparatus needs a boosting circuit (a boosting transformer: a transformer that is serially disposed on a line, and increases a voltage) for using the ultrasonic converter.
The related art vehicle ultrasonic parking assistance apparatus, as illustrated in FIG. 1, inputs a high voltage equal to or higher than a vehicle battery voltage to an ultrasonic converter 20 according to a turn ratio by using a transformer 10. In this case, a turn ratio of the transformer 10 and a ratio of an input voltage and an output voltage are as expressed in the following Equation (1):
                                          N            2                                N            1                          =                              V            2                                V            1                                              (        1        )            where N2 denotes the number of turns of wire on an output part, V2 denotes an output voltage, N1 denotes the number of turns of wire on an input part, and V1 denotes an input voltage.
Therefore, if a voltage output from a controller 30 is V1, the transformer 10 outputs a voltage
      “                            N          2                          N          1                    ⁢              V        1              ”    ,which passes through a matching circuit 40 and is input to the ultrasonic converter 20.
However, the transformer 10 applied to the related art vehicle ultrasonic parking assistance apparatus is based on an inductor on which a wire is wound, and thus has a limitation in reducing a size.
That is, since the transformer 10 occupies 5% or more of an area of a printed circuit board (PCB) equipped in the related art vehicle ultrasonic parking assistance apparatus, a size of the transformer 10 is relatively greater than that of a surface-mount device (SMD). Also, since the transformer 10 is high in height, the transformer 10 is not suitable for an element of an ultrasonic parking assistance apparatus for small vehicles.
In the transformer 10, when a turn ratio and a ratio of an input voltage and an output voltage are as expressed in the following Equation (2), power passing through the transformer 10 can be greatly lost according to a coupling coefficient K (0≦K≦1) used to determine a mutual inductance value.
                                          V            2                                V            1                          =                  K          ⁢                                    N              2                                      N              1                                                          (        2        )            
In the related art vehicle ultrasonic parking assistance apparatus including the transformer 10, a signal generation method performed by the controller 30 controls a current, and thus, a number of resources are needed for ideally implementing a variable current source 31 in the controller 30.
Moreover, the ultrasonic converter 20 is an element that converts a voltage into a sound pressure, and thus, when ten transmission signals are generated by a current driving scheme, as shown in FIG. 2, an output voltage can be distorted by a dispersion of the transformer 10. Also, a frequency of each of the generated transmission signals is broadly distributed as shown in FIG. 3, an output of a transmission frequency band is more lowered.
Generally, the transformer 10 used in a manufacturing process has ±3% error, and a frequency response of a transmission circuit can be changed by the error.
An application specific integrated circuit (ASIC) uses a digital filter having a high Q value for increasing a signal-to-noise ratio (SNR) of a reception signal. In this case, since the matching circuit 40 does not match a frequency of a transmission/reception signal due to the dispersion of the transformer 10, an end part of a free vibration signal in the ultrasonic converter 20 is greatly changed, and due to this, a defective ultrasonic parking assistance apparatus for vehicles that inaccurately recognizes a near object can be produced.
Moreover, an attenuation characteristic of an ultrasonic wave is differently shown according to an environment such as a temperature of a medium or the like, and unlike medical ultrasonic apparatuses, a use temperature range of a vehicle ultrasonic parking assistance apparatus is a range of −40 to 85 degrees C. Therefore, a level of a transmission voltage or an amplification rate of a reception signal should be changed according to an environment so as to obtain a predetermined level of reception signal regardless of the environment.
However, in the related art vehicle ultrasonic parking assistance apparatus, a level of an actual reflection signal is low, and thus, when greatly changing the amplification rate of the reception signal so as to obtain the predetermined level of reception signal, noise is also amplified. Due to the amplified noise, an occurrence probability of false alarm becomes higher.
To briefly summarize the above-described details, since the related art vehicle ultrasonic parking assistance apparatus uses the current driving scheme, the transformer 10 is needed for inputting a driving voltage to the ultrasonic converter 20. Also, since the transformer 10 has a broader area and a higher height than those of the SMD, the transformer 10 is not suitable as an element used to manufacture the related art vehicle ultrasonic parking assistance apparatus.
Moreover, the transformer 10 causes a loss of energy in a boosting operation, and a transmission signal can be distorted by a frequency response difference (caused by an inductance dispersion of the transformer 10) between the transmission frequency response and the matching circuit 40.